For the wet chemical treatment of work pieces, for instance for metal-coating or for etching, the work pieces are brought into contact with a treatment fluid, for example by immersion into a container containing the treatment fluid or by conducting a jet of the treatment fluid onto the surface of the work piece. The work pieces can be guided through a treatment system in a batch-wise manner or also by means of a continuous conveyor on which they are treated. During the treatment, the work pieces can be retained in an upright position or in a horizontal position. Printed circuit boards are, for example, typically treated either retained in the upright position in dip tanks or in a continuously operating system in which the work pieces are held in the horizontal position, being continuously conveyed. In the latter case, the treatment fluid can be kept in a stationary bath, the work pieces being guided through the said bath.
For wet chemical treatment it is typically advantageous for the treatment fluid to be set in motion during the treatment so that there is a sufficient fluid exchange on the surface of the work pieces to be treated and more especially in any small holes in the work pieces. Nozzles are used for this purpose, for example, the nozzle openings being disposed below the level of the fluid and conducting the fluid onto the surfaces of the work pieces. In addition, the fluid can also be set in motion by blowing air into the fluid.
The named measures for agitating the fluid have various disadvantages, the most important of which being that the movement of the fluid is too violent, which means that certain chemical processes, which ought to take place in the treatment fluid, do not take place or only take place insufficiently, and that the movement is frequently irregular, both as regards the time and the location. A strong influence on the fluid can result in its decomposition or at least in its damage.
To eliminate these disadvantages, U.S. Pat. No. 5,375,926 discloses an apparatus for mixing and distributing fluids in a container. The apparatus comprises a device generating oscillations, an oscillation shaft for the axial transmission of the oscillations generated by the device, at least one oscillating vane that is fastened to the oscillation shaft, and a mechanism for adsorbing the oscillations, which is disposed between the device generating the oscillations and a container. A plurality of oscillating vanes can be mounted on the shaft. The oscillating vanes are situated in a fluid in order to set the said fluid in motion.
In addition, Patent Abstracts of Japan to JP 08-281272A describes a device for treating liquid waste by means of electrolytic oxidation, for example, of used solution that has been used for the electroless deposition of nickel. The device includes three groups of electrode pairs, which are traversed by direct current. An agitating device that generates vibrations is disposed on one side of the electrode plates such that the flow in the fluid generated by the oscillations is interrupted by the groups of electrodes. To this end, an oscillating device is used where the oscillations of a vibration motor are transmitted to oscillating vanes by means of a retaining element. The vanes are inclined at an angle of 5°-30° relative to a plane that is perpendicular to the retaining element.
Further, US 2006/0141157 A1 discloses a plating apparatus for the treatment of a semiconductor wafer, this apparatus comprising an anode and a substrate holder holding the wafer. The apparatus additionally comprises a paddle (stirring rod) at a position facing a surface of the wafer and being disposed substantially vertically in the plating unit between the anode and the substrate holder. The paddle is configured to be moveable parallel to the wafer.
Further, US 2004/0217007 A1 discloses a method for plating comprising immersing a substrate, i.e., an article to form magnetic and non-magnetic materials that constitute the writing part of a read-write head, in a bath of plating solution and initiating an electrodeposition operation for depositing a layer of material on the substrate, the electrodeposition operation including agitating the bath and applying current to the substrate. Stirring is carried out by a reciprocating mixer which travels back and forth above the surface of the cathode at an approximate distance of 1/32 to ⅛ inch for providing agitation of the bath. The mixer is a paddle and has a pair of vertically elongate, triangular blades having spaced apart, parallel apexes defining there between a slot through which the fluid is flowable. The blades have oppositely facing, parallel, flat bases with one of the bases being disposed parallel to and closely adjacent to the substrate.
Further, US 2003/0155231 A1 discloses an electroplating apparatus comprising an electroplating bath, a pool of electrolytic solution inside the electroplating bath, a wafer immersed in the pool of electrolytic solution, a source metallic rod immersed in the pool of electrolytic solution, a regulation plate inside the electroplating bath in the space between the source metallic rod and the wafer and a paddle inserted in the space between the regulation plate and the wafer and immersed in the pool of electrolytic solution for mixing the electrolytic solution thoroughly.
Further, JP 2004162129 A relates to a plating apparatus and a method for enhancing the in-plane uniformity of the film thickness of a plating film by employing a dip system and adjusting the flow of plating solution in a plating tank. The apparatus comprises a plating solution injection nozzle to inject plating solution toward a surface to be plated of a work which is arranged perpendicularly inside the tank. The injection nozzle is disposed inside the tank and is disposed on a paddle which is disposed at the position facing the surface to be plated and moved along the surface to be plated to agitate the plating solution.
Finally, U.S. Pat. No. 4,258,653 discloses an apparatus for providing a dye density gradient to a web, the apparatus comprising a container which retains a dye bath, means for continually conducting the web longitudinally into the dye bath container and progressively transversely submerging the web in the dye bath and means for conducting the web out of the dye bath. The apparatus further comprises a frame of paddle with a plurality of paddles attached to the frame and means attached to the frame for moving the frame and the paddles in a reciprocating manner.
The known measures and devices for moving treatment fluid have various disadvantages: As already mentioned above, generating a movement in the fluid using the known devices and methods is very irregular which means that effects in the wet chemical treatment, which are dependent on the fluid flow, can be observed at different places and in different ways on the surface of the work piece. In addition, the generating of movements in the fluid using the known devices and methods, among other things, results in a very strong effect on the surface of the work piece, the said effect being restricted locally and/or only occurring sometimes. An efficient through-flow more especially of small holes is not possible by just using the known devices and methods. In addition, neither is it possible to obtain a flow over the surfaces of the work pieces in a targeted and controlled manner at a certain speed or in a certain direction. Moreover, the known devices and methods in many cases have the disadvantage of the mechanical structure being complex and consequently costly and requiring a large amount of energy for operation.